The present invention relates to a method for positioning and fixing electronic circuits disposed in layers upon a plurality of insulating circuit boards in a hot-pressing process, whereby several circuit boards are stacked so as to be congruent in their circuit layout and wherein elongated holes are provided in the area at the edge of the boards. The present invention also relates to a means for carrying out the method and to a device employing the means.
Multiple layer circuit boards are typically formed by pressing a plurality of circuit layers and bonding sheets held together by bolts in a vacuum whereby the boards are bonded together into so-called "multi-layers". The firm Fela Planungs AG offers a device for sale under the trademark "Multiklav" in which a plurality of assemblies of circuit layers are subjected to pressure and heat by a hydraulic fluid while in an evacuated bag made of a suitable elastomer, as disclosed in EP-A1-0 297 027. The individual circuit layers are stacked together with bonding sheets (prepregs) which are held in position temporarily during the press cycle by bolts extending through the elongated holes.
In practice, it has been shown that the elastomeric bags used in the "Multiklav" unit are exposed to extensive mechanical loads at the points in the stack where the circuit boards are held together by the bolts and for this reason wear out prematurely. If failure occurs during the pressing process, the enclosed boards are contaminated by the hydraulic oil.
Accordingly, an object of the invention is to provide a method and a means of carrying out the method so as to considerably lengthen the life of the bag and to exclude the danger of soiled boards due to hydraulic oil contamination.